The polyphenylene ether resins are well known in the art as a class of thermoplastics which possess a number of outstanding physical properties. They can be prepared, in general, by oxidative and non-oxidative methods, such as are disclosed, for example, in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358, which are incorporated herein by reference.
In is known that the polyphenylene ether resins alone are somewhat difficult to fabricate because of their high temperature thermoplastic molding characteristics and this has limited their use in applications where flexibility, such as the need to calendar into relatively thin sheets, without cracking or crazing, is desirable.
In recent years, there has also been increasing concern about the performance and safety of thermoplastic materials, including the afore-mentioned polyphenylene ether compositions during real-life fire situation.
Of particular interest would be a polyphenylene ether composition which is both flexibilized and flame retardant without loss of desirable properties.
It is known that flexible polyphenylene ether blends have been made with fairly high loadings of plasticizers. It has now been found that the capabilities and alternatives in making such blends can be greatly expanded by incorporating rubber in the form of a block copolymer into such blends, and further that if the flexibilizer is predominately an aromatic phosphate, good self-extinguishing properties are obtained.
Based on the foregoing discovery, it has also been found possible to further modify the blends to make them somewhat less costly, without loss of other beneficial properties, by replacing some of the aromatic phosphate with a halogenated hydrocarbon resin, e.g., chlorinated paraffin. Complete replacement of the aromatic phosphate is not possible, however, without loss of flame resistance.
Furthermore, based on the foregoing discovery, it has also been found possible to decrease the cost of the formulation, without introducing a halogen source, and at the same time, improve the self-extinguishing properties. This discovery comprises including alumina trihydrate in the composition.
Finally, based on the foregoing discovery, it has also been found possible to use higher levels of thermoplastic elastomer without disrupting flame retardant properties and still keeping a halogen-free system by the addition to the composition of elemental red phosphorus.
In addition to being useful by themselves, the new compositions are useful in blends with other resins and elastomers to improve flame retardancy. Of course, conventional additives such as pigments, fillers, stabilizers, and the like, can be used with the new compositions of this invention.